Opiate receptors were, for the first time, extracted from membranes in an active and soluble state. Solubilization was effected both from brain and neuroblastoma x glioma NG108-15 hybrid cell membranes. The solubilized receptors are large complexes with stokes radii of 70 A, and contain protein as an essential component. A new class of detergent, CHAPS, a zwitterionic (sulfobetaine) derivative of cholate was employed in these studies. Membranes from NG108-15 cells have continued to be useful for study of the dual regulation of adenylate cyclase by opiates and opioid peptides in cell-free systems. The purified membrane system appears to require the only addition of opiates, ATP and, probably, GTP. This is the simplest biochemical model of opiate tolerance and dependence developed to date.